This invention relates to vacuum packaging machines in general, more particularly to an improved sealing and evacuating station for vacuum packaging machines for producing sealed vacuum packages.
German published patent specification (Auslegeschrift) No. 1,939,216 discloses an evacuating and sealing station for vacuum packaging machines having upper and lower station portions, a heatable sealing member in one of said portions and a backing member in the other of said station portions, the sealing member and backing being movable one with respect to each other, an evacuating chamber being defined by the upper and lower station portions which is connected with a suction port connected with an evacuating system to evacuate the chamber in operation. The sealing member provided in the upper station portion may be moved by a pneumatic piston and cylinder device towards the backing and away therefrom in order to perform the sealing operation. The evacuation is performed through a suction port provided in a cover arranged over the sealing member. The air which will be sucked off from the evacuating chamber will flow across the edge portions of the heated sealing member.
Particularly when packaging food products with high water content, e.g. fresh meat, the generation of a high vacuum will produce large amounts of water vapour the volume of which will be multiplied by heating the water vapour upon contacting the heated sealing member. This seriously affects the evacuating operation and will result in either poor vacuum or the requirement of substantially increased capacity of the evacuating system.
The German utility model No. 7,221,634 discloses a similar device which is provided, on at least one side between the upper and lower packaging material foils, with a nozzle arrangement for supplying e.g. water vapour. If the upper packaging material foil is larger than the vacuum chamber, evacuation is performed through the nozzle arrangement, and simultaneously evacuation is performed through a connecting sleeve, because otherwise, the foils would contract and expel the material to be packaged because of the higher pressure in the upper chamber. In order to be able to provide the nozzle arrangement on one side between upper and lower foils, the upper foil is bulged upwardly in the region of the nozzle arrangement and towards the normal plane in the region of the sides. During evacuation, the aspirated gas or air will flow across the sealing member and be heated thereby, resulting in an increase of its volume requiring longer evacuation times at given capacity of the evacuation system.